The present invention relates to a method for thermally connecting the terminal areas of a contact substrate to the terminal areas of a carrier substrate, wherein the substrates are, in order to produce the connection, arranged in a connecting position such that the terminal areas are situated opposite one another in the plane of the connection, and wherein the contact substrate is heated to the connecting temperature from its rear side that is situated opposite the terminal areas in order to reach the required connecting temperature in the plane of the connection. The present invention also relates to a device that is suitable for carrying out this method.
In order to contact the terminal areas of a substrate with the terminal areas of another substrate, for example, to contact a chip on a carrier substrate, it is known to heat the chip from its rear side after it has been transferred into a connecting position in which it is connected to the carrier substrate and the chip terminal areas are situated opposite the assigned terminal areas of the carrier substrate. This is carried out in order to beat the chip terminal area arranged on the side situated opposite the rear side of the chip to the connecting temperature by means of thermal conduction, namely in such a way that a connecting material arranged between the chip terminal areas and the terminal areas of the substrate is heated to the melting temperature and an integral electric connection between the terminal areas is produced.
It is also known to utilize for this purpose connecting or contacting devices that contain a so-called xe2x80x9cthermodexe2x80x9d, i.e. an electric heating resistor that emits a high loss of heat when an electric current is applied, in particular, in a thermode contact region of usually tapered crosssection. This heat loss is utilized for heating the rear side of the substrate, e.g. the clip. Since the heat transfer from the thermode to the chip takes place in the form of thermal conduction, the thermal resistance between the different elements, i.e. the thermode and the chip, has disadvantageous effects on the time required for reaching the connecting temperature in the chip. With respect to practical applications, this means that, although the thermode can be heated to the required temperature within a few milliseconds, the time required for heating the chip to the connecting temperature amounts to a multiple thereof, in the region of 5-10 seconds, due to the thermal resistance between the thermode and the chip. The thermode contact region is also frequently deformed due to its high temperature load such that the surface contact with the chip is diminished and the thermal resistance that has disadvantageous effects on the heat-up time is further increased.
In addition, longer heat-up times of the chip that are caused by the significantly higher thermal capacity of the thermode in comparison to that of the chip can also be observed in practical applications.
Due to the long heat-up time required for reaching the connecting temperature in the chip or in the terminal areas of the chip, respectively, the known method is not suitable for use with substrates that are sensitive to high temperatures, e.g., substrates of PVC or polyester. Consequently, it is not possible to utilize the known method in the manufacture of chip cards, in which chips are arranged on carrier substrates of PVC, polyester or similar temperature-sensitive materials.
JP-A-60 162 574 describes a device for subjecting the rear side of a chip component to laser energy that is supplied via a glass fiber and focused by means of a lens. The chip component is held in position by a negative pressure device. The negative pressure device is realized separately of the glass fiber channel.
WO 97/12714 describes a device for selectively soldering in or soldering out components in a contactless fashion. In this device, the light of an infrared lamp is directed onto a component by a rigid quartz glass tube. The tube interior serves for subjecting the component to a vacuum such that the component can be held on the quartz glass tube.
U.S.-A-4,906,812 describes a soldering device in which the laser light is directed onto the soldering point by means of a glass fiber. A separate supply line and a separate discharge line for gases which lead to and from the soldering point are provided for transporting away soldering vapors.
JP-A-61 219 467 describes a device for mounting a flexible printed circuit board on another printed circuit board. The flexible printed circuit board is held by means of a vacuum device while the contact points are heated through separate channels by means of laser light supplied via a glass fiber.
JP-A-07 142 854 describes a device for attaching integrated circuits to a substrate. The electronic circuits are moved into the corresponding position and held therein by a vacuum pipette. The laser light emitted by a movably mounted laser heats the connecting lugs.
The present invention is based on the objective of proposing a method and a device which make it possible to produce a connection, of the initially described type also when temperature-sensitive substrates are used and to ensure that a particularly durable and stable connection is produced, namely while simultaneously sealing the contact region.
This objective is attained with a method and a device according to the invention. The contact substrate is heated due to the fact that laser energy acts upon the substrate. In this event, the energy introduction into the chip which is required for heating the contact substrate, e.g., the chip, is realized in the form of an absorption of the laser radiation in the chip, i.e., the thermal energy only manifests itself within the chip. In the method according to the invention, the thermal transmission resistance that results in the initially described disadvantages with respect to the heat-up time of the chip does not occur. This means that the heat-up time is significantly reduced such that a significantly lower thermal load for both substrates results. Consequently, the sensitive carrier substrate is not endangered, in particular, in the manufacture of chip cards. Due to the relatively low thermal load, the material of the carrier substrate can be selected according to needs. In addition to plastic substrates, even paper substrates may be considered. The risk of doping changes in the chip structure as they occur under excessively high thermal loads also is significantly reduced. Since the chip terminal areas are heated by heating the structure of the contact substrate, it is no longer necessary to focus the laser radiation onto the chip terminal areas, i.e., a corresponding focusing device can be eliminated. A displacement of an adhesive material arranged between the substrates in the plane of the connection takes place simultaneously with the arrangement of the substrates in the connecting position and the subsequent production of the thermal connection between the terminal areas of the substrates. This is particularly effective because a separate production step for subsequently sealing the gap between the substrates is no longer required. A connection between the two substrates which is particularly durable because it is protected from environmental corrosive effects can be achieved in this fashion.
Superior results, in particular, with respect to a largely uniform gap formation between the contact surfaces of the substrates can be achieved if the rear side of the contact substrate is supported during the heating of the substrate and the contacting of the substrate terminal areas that are situated opposite one another, with the support being realized in such a way that at least partial surface regions of the rear side are supported which lie outside of the energy surface upon which the laser energy acts.
The method according to the invention can be carried out in a particularly effective fashion if the support is at least partially realized with the aid of a contact surface of a contacting device that serves for connecting or for accommodating a glass fiber.
When carrying out the connecting method it has proved to be particularly advantageous to subject the substrate to a negative pressure via the contact surface in order to transfer the substrate into the connecting position. With such a measure, it is possible to produce the connection and to handle the contact substrate with one and the same device.
The contacting device according to the invention is for producing a thermal connection between the terminal areas of two substrates that are arranged opposite one another in a plane of connection. The contacting device is provided with a contact mouthpiece that serves for producing a connection with at least one glass fiber section. The contact mouthpiece contains a negative pressure device that is connected to a negative pressure opening in a contact surface of the contact mouthpiece. Due to this measure, the contacting device according to the invention not only makes it possible to heat the substrate by induction of the connecting heat in the substrate, but to also handle the substrate to be contacted. This means that a particularly effective production of the connection between the two substrates can be achieved.
The connection between the at least one glass fiber end section and the contact mouthpiece is realized with the aid of a fiber holding device, and the contact mouthpiece is provided with a number of glass fiber accommodation channels which corresponds to the number of glass fibers used, with the glass fiber accommodation channels opening into the contact surface such that a particularly exact alignment and defined arrangement of the at least one glass fiber end section relative to the contact substrate can be achieved. In this case, the fiber end crosssections of the glass fiber end sections may be arranged at a distance from the contact surface of the contact mouthpiece or flush with this contact surface.
The glass fiber accommodation channel or the glass fiber accommodation channels simultaneously serve for forming negative pressure lines of the negative pressure device, i.e., the contact mouthpiece can be designed in a particularly simple fashion.
In instances in which the fiber end cross-sections of the glass fiber end sections are, in particular, arranged flush with the contact surface of the contact mouthpiece, it is advantageous to provide the fiber holding device with a fiber advancing unit. This fiber advancing unit may be realized integrally with the fiber holding device or separately thereof.
The design of the contact mouthpiece can be further simplified if the fiber holding device is provided with a pressure connection for the negative pressure device such that the fiber holding device simultaneously fulfills two functions in this case.
An embodiment of the contacting device which has a particularly low maintenance requirement achieved if the fiber holding device serves for accommodating at least one glass fiber end section in such a way that a fiber end cross-section is arranged at a distance from the contact surface of the contact mouthpiece. Due to this measure, a direct contact between the fiber end cross-section and the substrate to be heated is prevented. Consequently, the fiber end cross-section is not heated such that possible soiling of the fiber end cross-section resulting therefrom is prevented.
If the contact mouthpiece is realized in the form of a capsule-like hollow body that contains the negative pressure opening in the contact surface and a pressure connection in its surface, an embodiment of the contacting device is achieved which is designed in a particularly simple fashion and can be easily manufactured.
Preferred variations of the method according to the invention and preferred embodiments of the device according to the invention are described in greater detail below with reference to the drawings.